DESCRIPTION this proposal is to gain further understanding of the cellular and molecular mechanisms that underlie the development of hypertrophy and heart failure in cardiomyopathy. Ca++ overload plays an important role in various cardiomyopathies. However, the primary mechanism for the abnormal regulation of cytosolic Ca++ is not well understood. The genetically determined cardiomyopathic hamster has been used as an animal model which closely resembles cardiomyopathy in humans. Recently, several studies have documented the pathogenetic role of abnormal sarcoplasmic reticulum (SR) function in congestive heart failure induced by various cardiomyopathies. The applicant's previous studies demonstrated that there are fundamental abnormalities of SR function and contractile function in cardiac myocytes from cardiomyopathic hamsters at the prehypertrophic stage. These abnormalities were apparent prior to a measurable increase in intracellular Ca++, and further developed in hypertrophy and heart failure stages. The applicant hypothesizes that an abnormality in the SR Ca++ release channel (CRC) may play an important pathogenetic role as the cardiomyopathic heart advances from prehypertrophy to heart failure. Using two distinct cardiomyopathic hamster strains, a) Bio 14.6 cardiomyopathic hamster, a strain which develops from hypertrophy to congestive heart failure; b) Bio 53.58 hamster, a strain which advances into congestive heart failure without the hypertrophic stage the applicant will: 1. Characterize the function of the SR and its pathogenic role in Ca++ homeostasis in the two cardiomyopathic hamster models at prehypertrophic, hypertrophic (or predilated and early dilated stages for Bio 53.58) and heart failure stages. The investigators will specifically examine: a) The rate of Ca++ uptake and release from the SR; b) The abnormal SR Ca++ release function effect on the rate and amplitude of the cell contraction. 2. Determine the mechanism of the abnormal CRC function in two cardiomyopathic models. They will examine: a) The number of affinity of the ryanodine binding sites; b) The CRC mRNA expression; c) The gating behavior of the CRC using the planar lipid bilayer technique; d) The CRC open probability affected by physiologic regulators and pharmacological regulators; and e) The molecular basis of the abnormal CRC in cardiomyopathies.